Synchronizing system



Oct. 24, 1939.

Filed March 24, 1937 2 Sheets-Sheet l 7 Z Y 9 I wz o 4 i v, 1 PE 1 4 ro 1 i 2 l z I i i fllfil 3 E i J, 8'. 1 8' 5 I I W H E B' 3 '5 1' M 1' 1 i7 I #5! i l |B 8 4 B 4 INVENTOR ROBERTANDRIEU ATTORNEY 35.; invention' 'Howsever r ii UNITED STATES PATENT OFFICE SYNCHRONIZIN G SYSTEM Robert Andrieu, Berlin,

Telefunken Gesellschaft graphie m. b. H., Berlin,

tion of Germany Application March 24,

Germany, assignor to fiir Drahtlose Tele- Germany, a corpora- 1937, Serial No. 132,721

In Germany March 24, 1936 4 Claims.

This invention relates to synchronizing methods, and in particular, to improved methods of synchronizing for interl such as used in television.

aced scanning systems The invention is concerned with the problem to synchronize the vertical impulse (change) in the re-creation of a television picture where interlaced scanning is used said interlacing method to be of a nature in whic mitted scans) to result in a co which the number of line each television picture in transmission. The shall here be assumed h the picture is transin two line series or sequences (or partial mplete frame, and in s per frame is odd. If

y consists of more than two sequences or partial scans, the number of lines per frame by the number of line sequences per frame should not be divisible without a remain der. The problem of synchronization of the vertical as in every other method, cal shift of one respective other scan is disturbance or distortion ture. Reference is no which Figs. 1 and 2 show imperfect interlaced impulse is particularly important on the nd that in the interlacing method mentioned,

even very slight vertipartial'scan in reference to the conducive to a serious of the television pic w made to the drawings, in

graphically perfect and scanning patterns respectively; Fig. 3 shows graphically a method of time distribution of synchronizing impulses according to the prior art for explaining the invention; Fig. 4 shows a time distribution of synchronizing impulses embodying the method of the invention;

Figs. 5 through 11 show'graphically load conditions in a television receiver for explaining the ing the accurate positio e are the demands regardn of the second line sequence or partial scan with respect to the first line sequence in the case of the interlaced scanning method shallbe explained more fully by ref ence to'Figs. 1 and2.

I, 3, 5, etc. belong to I, while'lines numbered 2,

tial scan II. Now, if the lines'of the second par-' cedwith accuracy into in tial scan fail to be tra the 'middle of the spaces Referring to Fig. 1, lines sequence or partial scan 4, 6', etc., make up parbetween the lines delineated by the first partial scan', and as shown in Fig. 2, they are displaced around from 5 to 10% (referred to the distance or spacing between two lines of the first partial scan) from the middle,

' such "paired position-of quite annoying in viewin exhibiting this trouble.

tance of 1 to 2 meters. vertical shift of the two li the lines will be found g a re-created picture That this is so can be readily verified by looking at Fig. 2 from a dis- The demand that the ne' sequences or partial scans in reference to each other should be less than 5% in the above defined sense means at the same time that the amplitude of the vertical sawtooth, for two consecutive sawteeth, for a 3'75-line picture, should be less than (5:375) percent or approximately 0.13 per thousand. It shall later be demonstrated that this demand is attended with certain difficulties.

In the invention hereinafter to be described, the further assumption shall be made that for the synchronization of the vertical impulse, several line impulses are skipped. Such a method which has been disclosed in an earlier co-pending specification U. S. Ser. No. 80,692, filed May 20, 1936 by Rudolf Urtel and entitled Synchronizing system offers the chance to make the vertical change or pulse rather precise and Well defined so that the two line sequences or partial scans in the re-created picture will present perfect accuracy to each other, in spite of the particular conditons which tend to aggravate the task of synchronization of the vertical pulse so difiicult in the interlaced method.

The special conditions obtaining in the interlacing method reside in the fact that, if two partial scans are assumed per complete frame (simple or two-lace method) the vertical pulse, in one partial scan, presents a distance or interval which is line longer in reference to the preceding line impulse than in the second sequence or partial scan. In other words, there is a risk that the means provided for filtering the vertical impulses from the line impulses, will act upon a given vertical impulse in a way slightly different from its response to the vertical impulse next following. This follows from the fact that at the instants of arrival of the two vertical impulses the state of the said filter or selector means is not the same because of the difference in antecedents as stated. According to the earlier invention in the above referred'to copending application, the said difilcultywas to be cured and overcome by the omission of a few line impulses prior to the vertical impulse. The circuit means designed to insure filtering of the vertical pulses is then able to adjust itself to a quiescent (inert) state so that uniform response to both vertical pulses may be anticipated.

However, it has been discovered that while the said scheme does improve the conditions surrounding the synchronization of the vertical pulse, relative shifts of the two line sequences in the re-created or incoming picture mayunder certain circumstances be caused, in other words, line positions such as indicated in Fig. 2 may happen.

The explanation of this occurrence has occasioned a good deal of difliculty for the reason that oscillographic investigations as well as calculations failed to reveal just why, in a situation as stated where a uniform response of the filter means to the vertical impulse had been safeguarded and assured, there was a possibility for the vertical deflection in the two line sequences or partial scans to differ.

Now, the idea which leads to a solution of the problem resides in the fact that the shape of the sawtooth serving for the vertical deflection is influenced as a result of the combined action of the following factors:

1. The sawtooth oscillator designed for line deflection shows an expenditure of current which is different when line impulses are fed to it than when there are no impulses.

2. The power pack (insuring supply from a line) and which furnishes all of the auxiliary voltages in television receivers, changes its output potential in the presence of load fluctuations.

3. Suppression of impulses, in the two-lace method, may be effected either in the manner that in both line sequences or partial scans an equal number of impulses are omitted so that the remaining impulse numbers of both partial scans becomes dissimilar, or else in the manner that in both partial scans an unequal number of impulses is omitted with the result that each line sequence or partial scan will contain the same number of impulses. In a simple or two-scan method, as has been noted, the number of lines per frame is odd so that to divide the corresponding line impulses over the two partial scans there are only the two ways and means that have been outlined above. 7

Now, it was to be surmised that with a view to insuring a uniform load for the power pack throughout the whole length of the frame it would be preferable to decide in favor of the second solution enumerated in (3) A closer examination, however, has brought out this extremely surprising result that it is incomparably far more satisfactory to work in each partial scan with an unequal number of impulses.

The research work in this direction shall hereinafter be discussed, with a view to simplifying considerations, under the assumption that the sawtooth oscillator for line deflection, upon each impulse, shows a consumption of current which is constant for the length of a line period and is thereupon of zero value.

In order to examine the building up of the picture in the vertical sense, which, as shall be shown, is tantamount to an investigation of the fall of potential across the power pack, there shall be examined the load of the power pack furnishing of the current for the sawtooth oscillator. For. it is quite easy to conceive that the power packv of the television receiver, in the absence of line impulses, shows zero voltage drop in the sense of the above supposition regarding the current consumption of the sawtooth generator.

To investigate the conditions of load in the power pack, reference is made to Fig. 3, where the shape of the line impulses for an entire frame is graphically represented, assuming a picture of 3'75 line definition and a two partial scan interlacing method. In order to simplify examinations, the first line sequence I is shown above the second sequence of lines or partial scan II. Each line sequence or partial scan consists of an in, terval which, in Fig. 1, has been designated as the vertical return; during this interval, as

comprises 182, and partial scan II only 181 line impulses. In other words, the conditions represented in Fig. 3 correspond to the first case mentioned under caption (3).

In Fig. 4 is shown the second instance mentioned in caption (3). The sole difference between this case and the one pictured in Fig. 3 is that the boundary E, F between the return and the "scansion in vertical direction is so placed that six impulses are suppressed in partial scan I, while only five impulses are suppressed in partial scan II. The result is that in partial scan I as many line impulses are handled as in partial scan II, that is, 182 each.

The sum total of suppressed and of transmitted line impulses, both in case Fig. 3 as well as in Fig. 4, amounts to 3'75, for it consists in the case of Fig. 3 to the sum of 6+182+6+18l impulses, while in Fig. 4 it is the sum of 6+182+5+182 impulses.

Upon the basis of the assumptions set forth in the beginning, namely, that the consumption of current of the sawtooth oscillator for line deflection, during the entire'line period (line return and line scansion) is to be constant and then zero, there are found conditions as indicated in'Fig. 5 for the case Fig. 3 so far as the load of the power pack by the sawtooth oscillator .is concerned. During line sequence or partial scan I the load of the power pack commences with impulse 1, and it terminates at the instant impulse I89 begins inasmuch as impulse E88 which belongs to the first line sequence, means a load for power pack which is to be constant for the period of one line and then zero. During the second line sequence II, on the contrary, the load starts only with impulse I95, which, like the rest of the impulse comprised in partial scan II, is positioned in the gap in reference to all other impulses of sequence I because of the odd number of lines'per frame. Impulse 194 still lies inside the vertical return (fiyback) time and thus causes no load. The end of the load in partial scan II is caused by impulse 315 and it lags line behind instant A, B.

Now, the load graph as shown in Fig, 5 contains a component which recurs with the fre quency of the partial scans (that is, a frequency of 50 cycles, and the even and the odd harmonics of 50 cycles, for a frame repetition frequency of 25 per second nowadays customarily used), and

also a component having only afrequency of 25 cycles. Fig. 5 readily shows that inside the time t1, t2, in partial scan I, and inside time interval in, t4. in partial scan II, the load of the power pack is entirely uniform. This load recurring at a frequency of 50 cycles could by no means he held responsible for a line shift or distortion such;

as shown in Fig. 2, seeing that it recurs at the same frequency at which the vertical change in and which lasts for a time equal to line, and a second load shock beginning 4 line after com pletion' of partial scan I, and which lasts also line. Within partial scan 11 there is no load,

unless the last-mentioned load shock is to be included in line sequence II. However, as shall later be shown it is wholly immaterial where this last-mentioned load shockis to be included; but for. the time being it shall be considered to be included in line sequence I although it happens in the time co-ordinated'to sequence II, that is, inside the vertical return of this sequence.

Before the 25-cycle load illustrated in Fig. 6 and which occurs in the method shown in Fig. 3, is examined more closely, there shall similarly be examined the case illustrated in Fig 4. In Fig. 7 the shape of the load curve inside partial scan I is the same as in Fig. 5. But inside sequence II, the load starts a line period earlier than in the case of Figs. 3 and 5. This is due to the fact that in Fig. 4, contradistinct to Fig. 3, impulse I94 is not suppressed and it terminates at the same instant as in Fig. 3 and Fig. 5, respectively. Also in this instance, the load components inside both partial scans which recur at a frequency of 50 cycles shall be eliminated from our further considerations, the residual 25-cycle load being shown in Fig. 8. A comparison of the load conditions for the method Fig. 3, on the one hand, and Fig. 4 on the other hand, leads to the finding that the curve is different in both cases, and that it occurs in a way as in Fig. 9 Where the load differences are shown by agraph' covering a who-1e frame period. Fig. 9 shows on the top abscissa the load differences according to'Fig. 6, that is, the load differences occurring when using the method of scanning indicated in Fig. 3, while below is shown the shape corresponding to Fig, 8 or the method indicated in Fig: 4. Now, it is to be noted that the load shocks on the top abscissa inrFig. 9 constitute a far lower 25 cycle period component than the load shocks in Fig. 9 in the lower abscissa, although in both cases there are two load shocks of like duration and equal amplitude. The fact that the load shown in the top abscissa in Fig. 9 is very much lower than in the lower abscissa of Fig. 9 may be deduced from the fact that the two shocks, in the tyo cases have a widely different phase to each other.

That this is so may be easily proved by the following consideration: Instead of Fig. 10 there shall first be investigated a load shock which differs from the one shown on top of Fig. 9 merely by that it is shifted in phase by 5 line periods. The load curve Fig. 10 accordingly must have the same absolute size of 25 cycle component as in Fig. 9 above. Only the phase of the 25 cycle component inside a frame may be different from that Fig. 9 above. On the other hand, it will be evident that a load curve as shown in Fig. 11 which also comprises two shocks of like amplitude and like duration as in Fig. 9 top or bottom and Fig. 10 can not contain any 25 cycle period component at all. Indeed, the two load shocks indicated in Fig. 11, figured from the instants A, B which are spaced th second apart, present like time intervals each of 5% lines. What is involved in Fig. 11 is a load recurring at a frequency of 50 (and higher harmonics), but not at afrequency of 25.

'It will, moreover, be evident that a 25 cycle period increasing from zero must be obtained if in the graph Fig. 11, the left one of the two load shocks is gradually shifted towards the end of the partial scan I and beyond as far as the right one of the two load shocks. As long as this shift is still small, as in the case of Fig. 10 (which, as stated, is identical with the top of Fig. 9), the 25 cycle component is small. But if the left one of the two load shocks is shifted in phase to a point close to the right shock, the 25 cycle component becomes much greater. But what is obtained in this latter case is the same load distribution as shown below in Fig. 9, and this proves the accuracy of the above statement that the amplitude of the 25 period component shown on the lower abscissa in Fig. 9 is greater than that shown on the top abscissa in Fig. 9. The phase position of the 25 cycle component in Fig. 9 above, to be sure, differs from the one below, though this has no effect upon the described difierence in the amounts of the amplitudes.

A Fourier series analysis of the curves of the loads in both cases also demonstrates that the 25 cycle load component in the case of the lower abscissa Fig. 9 below is approximately 10 times greater than in the upper abscissa Fig. 9.

By reference to Fig. 9 it must be re-emphasized that it is extremely surprising that the suppression of impulse l 94 should excercise such a pronounced effect upon the size of the 25 cycle load component, though it will be seen that this fact and feature is the sole difierence between the method depicted in Fig. 3 and that in Fig. 4.

Now, the 25 cycle load component is responsible for the vertical distortion and relative shift of the two partial scans in the incoming picture because the power pack (power converter means) furnishes to the vertical sawtooth oscillator, in the second partial scan, a different direct current voltage than it furnishes during the first partial scan. The vertical deflection during the second scan or line sequence, therefore, obeys a slightly different law than during the first partial scan, and the consequence is that the lines delineated during the second line sequence are unable to fall exactly in the middle between the lines of the first time sequence, if the drop of potential of the power pack fluctuates at a frequency of 25 cycles. In actual practice, however, it has been found that the voltage variation in the case of Fig. 3 is so slight (it having been stated already that it is about 10 times less than in the case of Fig. 4), that its effect is negligible.

Whence the technical rule embodied in this invention, namely, to eifect the suppression of line impulses sothat one line sequence or partial scan should include one more line impulse than the other partial scan, and that for each vertical change an equal number of line impulses should be omitted. The method embodied in Fig. 4 in which both partial scans contain a like number of impulses, while in one partial scan one more impulse is omitted than in the respective other partial scan, occasions, in contrast to the method Fig. 3, such a marked load for the power pack of a frequency of 25 cycles that the resultant fluctuation of voltages very appreciably impairs the building up of the television picture in the vertical sense. And this distortion would be still further aggravated, if, for instance, in the second partial scan the difference in the number of suppressed impulses were to be chosen still greater than one.

Another point which must be emphasized is that the conditions as hereinbefore described are entirely independent of whether the sawtooth generator for line deflection, upon the occurrence or else in the absence of line impulses, shows a higher current consumption. The former case has been tacitly assumed to exist above in that the load of the power pack has been examined. The latter case may be traced back to the former by examining the load relief, in other words, the change in potential of the power pack caused by the lower current consumption upon an occurrence of line impulses. So far as the relative size of the 25 cycle component is concerned, the identical result is obtained in both cases.

It must also be pointed out that in a threescan interlacing method, and a vertical frequency of 50 C. P. 5., two disturbing frequencies, i. e., of 16% and of 33 C. P. S. would occur instead of one frequency of 25 C. P. S.

It is to be pointed out in conclusion that the vertical change impulse which must be transmitted during the vertical flyback in some form or another may cause a fluctuation of voltage in the power pack by no means of a frequency of only 25, or of 16 and 33 /0, C. P. S., regardless of the particular way in which it is transmitted and evaluated at the receiving'end.

Having described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In the method of synchronizing interlaced scanning systems, the steps of generating a first sequence of a predetermined number of impulses during a predetermined time interval, suppressing a predetermined number of the first generated impulses, generating a second sequence of impulses differing by unity from the predetermined number cf the first sequence of impulses during a time interval equal to the said predetermined time interval, suppressing a predetermined number of the second generated impulses differing by unity from the predetermined number of the first suppressed impulses, and transmitting sequentially the" unsuppressed impulses of the first sequence and the unsuppressed impulses of the second sequence.

2. In the method of synchronizing interlaced scanning systems, the steps of generating a first sequenceof a predetermined number of impulses during a predetermined time interval, suppressing a predetermined number of the first generated impulses, generating a second sequence of impulses differing from the predetermined number of the first sequence of impulses during a time interval equal to the said predetermined time interval, suppressing a predetermined number of the second generated impulses differing from the predetermined number of the first suppressed impulses, and transmitting sequentially the unsuppressed impulses of the first sequence and the unsuppressed impulses of the second sequence.

3. In the method of synchronizing interlaced scanning systems, the steps of generating a first sequence of a predetermined number of impulses during a predetermined time interval, suppressing a predetermined number of the first generated impulses, generating a second sequence of impulses differing from the predetermined number of the first sequence of impulses during a time interval equal to the said predetermined time interval, suppressing a predetermined number of the second generated impulses differing from the predetermined number of the first suppressed impulses, and transmitting sequentially unsuppressed impulses of the first and second sequences. 7

4. In the method of synchronizing interlaced scanning systems, the steps of'generating a first and second sequence of impulses during equal time intervals, said first sequence having one more impulse than the second sequence, suppressing generated impulses of the first and second sequence during equal time intervals, said second sequence having one less impulse suppressed than said first sequence, and transmitting sequentially the unsuppressed impulses of the first and sec-' ond sequence.

ROBERT ANDRIEU. 

